1978-1987 BMW 633CSi,733i 528e 735i AC Condenser Relay Testing

  Let me preface this post by saying that I'm no electrical guru. I'm an IT Analyst with an interest in electronics. Enough interest to want to learn and discover more about how and why things work the way they do.

  In lue of that, today finds me checking out some relays for PartsEuropean.com. Good people over there. This all spawned from some supposedly bad relays that were reported by an eBay buyer. Time to pull out the ole multi-meter and have a gander.

  We are working on an 1978-1987 BMW 633CSi,733i 528e 735i AC condenser relay specifically. There was some talk of these not being in proper working order. Let's give this thing a once over and see if we can find out.

  Trying to cross reference part numbers for these guys is hard. Even realoem.com's site seemed to turn up empty. It needs a 7 or an 11 digit number. All the numbers on this thing are neither. Hmm...

  Testing resistance across the terminals lead me to these conclusions on two separate multimeters:

  I tested three of them to almost exactly identical specs, within 0.3k. 

  The relay actually has a mechanical relay inside. That giant copper colored piece has a switch that is moved when the relay is triggered. 

  Here we can see the actual relay switch contact.

  The micro chip inside the relay. It has 7 terminals on the bottom. 

  There are several components on this board. Here is what I can make of them. Those two at the top right actually turned out to be diodes. The resistance on the 180K resistor checks out. This is between pins 6 and 3.

  I found a diagram from an aftermarket unit that looks like this. Here is my crude diagram of such.

  I can vouch for Pins 4 and 5, they do in fact change when the relay is triggered.

  Based on all that I can make out of this, there is no reason to think that this relay is no functional. If someone else out there has more information on this please comment. I'm always happy to learn more. Two heads are better than one in many cases!